Surface switchable photoresist

ABSTRACT

Lithography methods on a semiconductor substrate are described. The methods include coating a resist layer on the substrate, wherein the resist layer comprises a resist polymer configured to turn soluble to a base solution in response to reaction with an acid, and a switchable polymer that includes a base soluble polymer having a carboxylic acid, hydroxyl, lactone, or anhydride functional group, performing a pre-exposure bake on the resist layer, exposing the resist-coated substrate, and developing the exposed substrate with a developing solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/534,289, which was filed on Sep. 22, 2006, the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The present disclosure relates generally to resist materials, such ascan be used in immersion or non-immersion photolithography, or otherprocesses used in the manufacture of semiconductor integrated circuits.

Lithography is a mechanism by which a pattern on a mask is projectedonto a substrate such as a semiconductor wafer. In areas such assemiconductor photolithography, it has become necessary to create imageson the semiconductor wafer which incorporate minimum feature sizes undera resolution limit or critical dimension (CD). Currently, CDs arereaching 65 nanometers and less.

Semiconductor photolithography typically includes the steps of applyinga coating of photoresist (also referred to as resist) on a top surface(e.g., a thin film stack) of a semiconductor wafer and exposing thephotoresist to a pattern. The semiconductor wafer is then transferred toa developing chamber to remove the exposed resist, which is soluble toan aqueous developer solution. As a result, a patterned layer ofphotoresist exists on the top surface of the wafer.

Immersion lithography is a new advance in photolithography, in which theexposure procedure is performed with a liquid filling the space betweenthe surface of the wafer and the lens. Using immersion photolithography,higher numerical apertures can be built than when using lenses in air,resulting in improved resolution. Further, immersion provides enhanceddepth-of-focus (DOF) for printing ever smaller features. It isunderstood that the present disclosure is not limited to immersionlithography, but immersion lithography provides an example of asemiconductor process that can benefit from the invention described ingreater detail below.

The immersion exposure step may use de-ionized water or another suitableimmersion exposure fluid in the space between the wafer and the lens.Though the exposure time is short, the fluid can cause heretoforeunforeseen problems. For example, droplets from the fluid can remainafter the process and can adversely affect the patterning, criticaldimensions, and other aspects of the resist.

One solution to help reduce defects, such as watermark defects, is touse a top coat layer on the resist layer. One such example is shown inU.S. Pub. No. 2006/111550, which is hereby incorporated by reference.However, the addition of a top coat layer provides additional concerns,and adds an additional layer to the entire process which increasesoverall production cost.

This application is related to U.S. application Ser. No. 11/324,588filed Jan. 3, 2006 entitled, “Novel TARC Material for ImmersionWatermark Reduction”, which is hereby incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flow chart of a method for implementing a lithographyprocess with reduced defects, according to one or more embodiments ofthe present invention.

FIGS. 2-4 are side cross-sectional views of a semiconductor wafer thatis being processed by the method of FIG. 1.

FIGS. 5-8 are side cross sectional views of a semiconductor wafer thatis experiencing a benefit from at least one embodiment of the presentinvention.

FIG. 9 is a side cross sectional view of a semiconductor wafer that isexperiencing a benefit from another embodiment of the present invention.

FIG. 10 is a side cross sectional view of a semiconductor wafer that isexperiencing a benefit from yet another embodiment of the presentinvention.

FIGS. 11-13 are side cross sectional views of a semiconductor wafer thatis experiencing a benefit from another embodiment of the presentinvention, being used in an immersion lithography system.

FIG. 14 is a side cross sectional view of a semiconductor wafer that isexperiencing a benefit from yet another embodiment of the presentinvention, also being used in an immersion lithography system.

FIGS. 15-18 are chemical diagrams of a switchable polymer material foruse in one or more embodiments of the present invention.

DETAILED DESCRIPTION

The present disclosure relates generally to the fabrication ofsemiconductor devices, and more particularly, to a method and system forpreventing defects in a semiconductor substrate. It is understood,however, that specific embodiments are provided as examples to teach thebroader inventive concept, and one of ordinary skill in the art caneasily apply the teachings of the present disclosure to other methodsand systems. Also, it is understood that the methods and systemsdiscussed in the present disclosure include some conventional structuresand/or steps. Since these structures and steps are well known in theart, they will only be discussed in a general level of detail.Furthermore, reference numbers are repeated throughout the drawings forthe sake of convenience and example, and such repetition does notindicate any required combination of features or steps throughout thedrawings.

The following disclosure is separated into three sections. The firstsection describes an example of a lithography process that can benefitfrom one or more embodiments of the present invention. The secondsection describes how a switchable polymer layer used in the lithographyprocess discussed above reacts and changes during the lithographyprocess. The second section also discusses various benefits from thedifferent embodiments, it being understood that additional and/ordifferent benefits may further exist in other embodiments of the presentinvention. The third section describes several different embodiments ofswitchable polymer material that can be used to create the switchablepolymer layer.

The Lithography Process

Referring to FIG. 1, a simplified flowchart of a method for lithographywith a reduced number of defects is designated with the referencenumeral 100. The lithography method 100 is but one example of a processthat can benefit from one or more embodiments of the present invention.In furtherance of the present example, the lithography method 100 willbe described as an immersion lithography process. The method 100 willfurther be discussed and illustrated with FIGS. 2-4 to show an examplewafer 200 being processed by the method. The wafer 200 includes asubstrate 212, which may further include one or more layers, includingpoly, metal, and/or dielectric, that are desired to be patterned.

Referring to FIGS. 1 and 2, the immersion lithography method 100 beginsat step 102, where the wafer substrate 212 is coated with a layer ofresist 214. The resist 214 is a two- or multi-component resist system.The application of the resist 214 may be done with spin-coating oranother suitable procedure. Prior to the application of the resist, thesubstrate 212 may be first processed to prepare it for thephotolithography process. For example, the wafer 200 may be cleaned,dried and/or coated with an adhesion-promoting material prior to theapplication of the resist. At least a portion of the resist 214 includesswitchable polymer material for creating a switchable polymer layer.Example characteristics and compositions of the switchable polymer layerare discussed in greater detail in the following two sections.

Referring to FIGS. 1 and 3, the immersion lithography method 100proceeds to step 104, where a pre-bake process is performed. The wafermay be heated to a temperature of about 85 to about 150° C. for about 30to about 200 seconds, for example. As shown in FIG. 3, switchablepolymer material moves, diffuses, or is otherwise formed in an area ofthe resist 214 opposite to the substrate 212. For the sake of furtherdescription, the area of the resist 214 in which the switchable polymermaterial resides is referred to as the switchable polymer layer 214 a.

The immersion lithography method 100 proceeds to step 106, where animmersion lithography exposure is performed. The wafer 200, includingthe resist 214, are immersed in an immersion exposure liquid (e.g.,deionized water) and exposed to a radiation source through the lens(FIG. 2). The radiation source may be an ultraviolet light source, forexample a krypton fluoride (KrF, 248 nm), argon fluoride (ArF, 193 nm),F2 (157 nm), extreme ultra-violet (EUV, 13.5 nm) and e-beam laser. Theresist 214 is exposed to the radiation for a predetermined amount oftime, dependent on the type of resist used, the intensity of theultraviolet light source, and/or other factors. The exposure time maylast from about 0.2 seconds to about 30 seconds, for example. Theexposure results in portions of the resist becoming solid, while otherportions remaining in a fluid state. It is understood that a negativeresist can also be used, with inherent differences. Following theexposure process, one or more treatment process may be performed to helpreduce the number of water droplets or other defects that may arise.

The immersion lithography method 100 proceeds to step 109, where thewafer 200 with the exposed resist 214 is heated with a post-exposurebake (PEB) for polymer dissolution. This step lets any generated photoacid (or base) react with the polymer and facilitate the polymerdissolution. The wafer 200 may be heated to a temperature of about 85 toabout 150° C. for about 30 to about 200 seconds, for example.

Referring to FIGS. 1 and 4, the immersion lithography method 100proceeds to step 110, where a pattern developing process is performed onthe exposed (positive) or unexposed (negative) resist 214 to leave adesired mask pattern 216. The wafer 200 is immersed in a developerliquid for a predetermined amount of time during which a portion of theresist 214 is dissolved and removed. The wafer 200 may be immersed inthe developer solution for about 5 to about 60 seconds, for example. Aseparate, additional rinse may also be applied. After being immersed inthe developer solution, the resist pattern surface loses about 50 A ofits previous height, due to the removal of the switchable polymer layer.The composition of the developer solution is dependent on thecomposition of the resist, and is understood to be well known in theart. A base solution of 2.38% tetramethyl ammonium hydroxide (TMAH) isone example of a developer solution.

The Switchable Polymer Layer

Different embodiments of the switchable polymer layer can provide one ormore benefits to the lithography operation described above. Several ofthese benefits are further discussed below. Additional benefits may alsoexist, and no particular benefit is required for every embodiment of theswitchable polymer layer.

Referring now to FIGS. 5-8, one benefit is that the switchable polymerlayer helps to remove particles from the wafer's surface. In FIG. 5, awafer 300 is shown having a resist layer 314. The resist layer 314includes a switchable polymer layer 314 a according to one or moreembodiments of the present invention. The wafer has been through animmersion lithography process, and has a defect 320 on a top surface.The wafer is then provided to a development process, which isillustrated in FIGS. 6-8.

In FIG. 6, a developer solution 330 is applied over the top surface ofthe wafer. As shown in the figure, the developer solution 330 hasalready removed a portion of the switchable polymer layer 314 a that wasnot immediately under the defect 320. As shown in FIG. 7, after anadditional amount of time has transpired, the developer solution 330 haspenetrated and removed more of the switchable polymer layer 314 a thatis under the defect 320. As shown in FIG. 8, eventually the switchablepolymer layer 314 a is sufficiently removed so that the defect 320completely separates from the rest of the resist layer 314. The defect320 can be washed away with the developer solution or a rinse, orremoved by other means.

It is understood that although the resist layer 314 is not illustratedas having a specific pattern (like that shown in FIG. 4), the resistlayer can indeed be patterned, and the present figures only show a smallportion of a larger resist layer. The defect 320 can be on a solidportion of resist 314, or may cover several patterns and spaces ofresist after the resist is developed. In both instances, the resultingpatterned resist layer has reduced defects, as compared to a moreconventional resist. It is also understood that although some of theswitchable polymer layer 314 a was removed by the developer 330,additional portions of the layer of switchable polymer material maystill exist in the patterned and developed resist layer 314. Theadditional portions of the switchable polymer material can later beremoved, such as through a water rinse operation. The defect 320 issurrounded with soluble polymer that has a good affinity to water, whichmakes it easy to remove.

There are several potential mechanisms that prevent the defect 320 fromre-adhering to the surface of the resist 314. One mechanism is due tosurface charging. Both the defect 320 and the resist layer 314 develop acommon charge from an ionic group on the outer surface of each. Theionic charge may come from a surfactant in the developer, or thedeveloper used in the developing process. Since both charges are thesame (e.g., positive), the defect 320 is naturally repelled form theresist layer 314. Another mechanism is that both the outer surface ofthe defect 320 and the outer surface of the resist 314 have hydrophilicpolymer bonding. A hydrophilic group is attached to a polymer backboneon each surface, thereby discouraging bonding between the two groups ofdifferent surfaces. The hydrophilic polymer may come from a surfactantin the developer solution, or a developer polymer from the switchablepolymer layer, or from another polymer produced during the developmentprocess.

Referring to FIG. 9, another benefit is that isolated pattern areas willbe less likely to include a watermark defect. In one embodiment, a wafer400 includes a substrate 412 having a resist layer 414. The resist layer414 includes a switchable polymer layer 414 a according to one or moreembodiments of the present invention. As shown in the figure, there is adense pattern area 416 and an isolated pattern area 418. With aconventional resist, the dense pattern area would be more hydrophilic,and the isolated pattern area would be more hydrophobic. However, byusing the switchable polymer layer 414 a, both areas 416, 418 have amore hydrophilic surface. That is, in addition to becoming soluble to(or after contact with) a TMAH developer solution, the switchablepolymer layer 414 a has become hydrophilic without the need of exposure.As a result, the hydrophilic nature of the isolation pattern area 418encourages the removal of any watermark defect 420.

Referring to FIG. 10, yet another benefit is that all pattern areas willbe less likely to include a watermark defect. In one embodiment, a wafer500 includes a substrate 512 having a resist layer 514. The resist layer514 includes a switchable polymer layer 514 a according to one or moreembodiments of the present invention. The switchable polymer layer 514 acontains an acid 516 which can prevent watermark formation. Exposedareas of the resist 514 are prevented from leaching (identified byarrows 518) to interact with a water drop 520, thereby furtherpreventing watermark formation. The switchable polymer 514 a can alsorinse away from the top surface of the resist 514 to reduce thewatermark defect and to also prevent any scum that would otherwisebridge over proximate non-exposed areas of resist that were, at onetime, covered by the water drop 520.

Referring to FIG. 11, another benefit is that there are reduced defectsthat reside on a wafer surface from the immersion lithography process.For example, a wafer 600 can be provided to an immersion lithographysystem 610 for creating patterns on a resist layer 614 of the wafer. Theresist layer 614 includes a switchable polymer layer 614 a according toone or more embodiments of the present invention. The wafer 600 includesone or more wafer surface defects 620. The immersion lithography systemincludes a lens system 622, a structure 624 for containing a fluid 626such as de-ionized water, various apertures 628 through which fluid canbe added or removed, and a chuck 630 for securing and moving the wafer600 relative to the lens system 622. The fluid containing structure 624and the lens system 622 make up an immersion head. The immersion headcan use some of the apertures as an “air purge,” which can add airtowards the wafer for drying, and other apertures for removing anypurged fluid. Normally, any defects induced during the immersion processcan dry in a few seconds time, and the resulting Vanderwaal forcesbetween the defect and the resist make it very difficult to remove laterby the immersion water.

Referring also to FIGS. 12-13, in the present embodiment, the defect 620starts to dry, but a surface 630 that is adjacent to the switchablepolymer layer 614 a maintains a wet condition. The adjacent surface 630includes hydrogen bonding which is hydrophilic and can be easilypenetrated with the immersion fluid 626. As a result, the hydrogenbonding and immersion fluid 626 make the defect 620 more easilyseparable from the resist 614 and removable during the immersionlithography process.

The hydrogen bonding, and the resulting hydrophilic surface, can resultfrom several factors. One factor is that the switchable polymer materialincludes a surfactant which can diffuse to the resist surface afterapplying the resist to the wafer surface or after baking the resist. Thesurfactant can achieve a low contact angle and absorb water/moisturebetween the defect 620 and the resist 614. Another factor is that theswitchable polymer material includes a hydrogen bonding functional groupwhich can absorb the immersion fluid 626 inside the resist surface.Another factor is that the switchable polymer layer that is water-rich(from the immersion fluid 626) has a thickness substantially more than10 A, with a preferred thickness of about 150 A.

Referring to FIG. 14, another benefit is that there is reduced surfacemoisture in the resist after an immersion lithography process. For thesake of continued example, the immersion lithography system 610 of FIG.11 is shown, as well as a wafer 700 including a substrate 712 and aresist layer 714. The resist layer 714 includes a switchable polymerlayer 714 a according to one or more embodiments of the presentinvention. After contact with the immersion fluid 626 (e.g., water) inthe immersion head, the resist 714 contains a large amount of water. Theabsorbed water evaporates into the air, and such evaporation absorbs theresist heat and reduces the resist surface temperature. The localtemperature change influences a focus sensor on the immersion head.However, in the present embodiment, the switchable polymer materialprovides a water-absorbing compound into the resist and traps the waterwith less evaporation and less thermal change after immersion waterscanning. As a result, better focus control is provided to the focussensor.

The Polymer Material

In the present embodiments, the resist (214, 314, 414, 514, 614, and/or714) includes at least two types of material, a standard resist polymermaterial and a switchable polymer material. The standard resist polymermaterial turns soluble to a base solution in response to an acid. Thestandard resist polymer material may include a photo acid generator(PAG) to produce the acid, thereby supporting a chemical amplifiedreaction (CAR). CARs are often used in deep ultraviolet (UV) and deepsubmicron technologies. During lithography, a photon inducesdecomposition of the PAG and forms a small amount of acid. The formedacid induces a cascade of chemical transformations in the resist film,typically during a post-exposure bake step. It is understood that thereare many other examples of resist, including those with a photo basegenerator (PBG). Also, whether the resist is positive resist or negativeresist is a matter of design choice, but for the sake of furtherexample, a positive resist with PAG will be described.

The switchable polymer material is an additive to the standard resistmaterial, and includes properties that cause it to separate from atleast some of the standard resist material and diffuse or move towardsan upper surface (as shown in the drawings) of the resist during apreliminary process. The switchable polymer material also includesproperties that are important to a later processing operation, such asbeing easily removed in response to a developer solution or water rinse,or turning hydrophilic in an immersion fluid.

There are several ways that additive material can diffuse to the resistsurface, one or more of which can be used, as a choice of design. Oneways is due to a molecular weight difference. The switchable polymermaterial has a lower molecular weight than the resist material, whichcauses the polymer material to diffuse into the top area of the resistduring the pre bake process. Another way is due to a polaritydifference. The switchable polymer material has a different polarity,which causes the polymer material to diffuse into the top area of thereresist during the pre bake process. For example, if the resist film ismore non-polar as compared to the switchable polymer material, the twopolarities of film will separate after thermal baking. Another way is ahydrophilic/hydrophobic difference. If the switchable polymer materialhas a different hydrophilic/hydrophobic ratio, the solubility to solventor to each other will also different. The switchable polymer materialwill separate from other material during the thermal baking process. Yetanother way is a difference in solubility to a solvent. If theswitchable polymer material solubility to a solvent is higher than theresist polymer, then the additive polymer can diffuse into the top areaof the resist along with the solvent during the pre bake process.Another way is due to polymer solubility. If the switchable polymermaterial and the resist material have different hydrogen bonding orVanderwaal forces with each other, this difference will cause the twomaterials to separate after thermal baking.

In one embodiment, the switchable polymer is an acid labile polymer thatwill react, e.g., become soluble, after being exposed to a solution suchas developer solution. The switchable polymer may be soluble to water,to the developer solution, or both. The switchable polymer turns solubleto water after releasing a leaving group in a reaction with an acidproduced from the resist (PAG) or the developer solution. The acidlabile polymer material can include base quenchers to diffuse into theresist to stop or significantly reduce photo acid generation in a CAR,such as during PEB.

In another embodiment, the switchable polymer material is a base solublepolymer that becomes water soluble after reacting with a solution suchas a developer solution. An example of a base soluble polymer is acarbonyl group such as provided in FIG. 15, where R1, R2 and R3 each arehydrogen, a fluorine atom or a straight, branched or cyclic alkyl orfluorinated alkyl group of 1 to 20 carbon atom, R4 is a straight,branched or cyclic alkyl or fluorinated alkyl group of 0 to 20 carbonatom. Another example of a base soluble polymer is a hydroxyl group suchas provided in FIG. 16, where R5, R6 and R7 each are hydrogen, afluorine atom or a straight, branched or cyclic alkyl or fluorinatedalkyl group of 1 to 20 carbon atom. R8 is a straight, branched or cyclicalkyl or fluorinated alkyl group of 1 to 20 carbon atom. Another exampleof a base soluble polymer is a lactone group such as provided in FIG.17, where R9, R10 and R11 each are hydrogen, a fluorine atom or astraight, branched or cyclic alkyl or fluorinated alkyl group of 1 to 20carbon atom, R12 and R13 each are a straight, branched or cyclic alkylor fluorinated alkyl group of 1 to 20. Another example of a base solublepolymer is an anhydride group such as provided in FIG. 18, where R14,R15 and R16 each are hydrogen, a fluorine atom or a straight, branchedor cyclic alkyl or fluorinated alkyl group of 1 to 20 carbon atom, R17and R18 each are a straight, branched or cyclic alkyl or fluorinatedalkyl group of 1 to 20. The switchable polymer layer formed from thebase soluble material can have a thickness between about 10 A to about3000 A, with a preferred thickness between about 10 A and about 1000 A.Also, after developing, the overall reduction of height of theswitchable polymer layer can be less than 500 A, and more preferablyless than about 50 A or 30 A.

Additional examples of the switchable polymer material include:

-   -   Carboxylic polymer: RCOOH+OH—=>RCOO—+H2O;    -   Acid sensitive leaving group: RCOOR1+H+=>RCOO—;    -   Fluoride polymer: RC(CF3)2OH+OH—=>RC(CF3)2O—;    -   Hydroxyl contained polymer: ROH+OH—=>RO—; and    -   Lactones, anhydride contained polymer RCOOR1+OH1=>RCOO—+R1OH.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention.

In one embodiment, a material is provided for use in lithographicprocess of a semiconductor substrate. The material includes aphoto-sensitive polymer configured to turn soluble to a base solution inresponse to reaction with an acid and at least one of either a basesoluble polymer or an acid labile polymer. The base soluble polymer isconfigured to turn soluble to water in response to reaction with adeveloper solution. The acid labile polymer is configured to turnsoluble to water after releasing a leaving group in reaction to theacid.

In some embodiments, the material further includes a photo acidgenerator configured to release the acid in response to opticalexposure, and/or a quencher base for reacting with the acid.

In some embodiments, the acid labile polymer further comprises at leastone of an adhesive group or an etching resistance group. In someembodiments, the base soluble polymer includes a polymer group of eithera carbonyl group, a hydroxyl group, a lactone group, or an anhydridegroup.

In another embodiment, a method for performing lithography on asemiconductor substrate is provided. The method includes coating aresist on the substrate to a first height, performing a pre-exposurebake on the resist, exposing the resist-coated substrate, and developingthe exposed substrate with a developing solution. During thepre-exposure bake, the resist is substantially separated into a firstlayer and a second layer. After developing, the resist has a secondheight of at least 50 A less than the first height.

In some embodiments, the step of coating the resist includes combining afirst polymer material that does not become water soluble after beingdeveloped with the developing solution, and a second polymer materialthat does become water soluble after being developed with the developingsolution.

In another embodiment, a resist material for use with a substrate isprovided. The resist includes a first polymer material and a secondpolymer material. The first polymer material is configured to diffusefrom the second material and towards an exterior surface of thesubstrate during a baking operation. The first polymer material is alsoconfigured to change properties when exposed to a solution.

In some embodiments, the first polymer material is configured to becomemore hydrophilic when exposed to an immersion fluid used in an immersionlithography system.

In some embodiments, the first polymer material is configured to becomemore water-soluble when exposed to a developing solution.

It is understood that various different combinations of the above-listedembodiments and steps can be used in various sequences or in parallel,and there is no particular step that is critical or required.Furthermore, features illustrated and discussed above with respect tosome embodiments can be combined with features illustrated and discussedabove with respect to other embodiments. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

We claim:
 1. A method for performing lithography on a semiconductorsubstrate, the method comprising: coating a resist layer on thesubstrate, wherein the resist layer comprises a resist polymerconfigured to turn soluble to a base solution in response to reactionwith an acid, and a switchable polymer that includes one of:

wherein R1, R2, and R3 are H and R4 is a fluorinated alkyl group of 1 to20 carbon atoms; R5, R6, and R7 are H and R8 is a straight chainfluorinated alkyl group of 1 to 20 carbon atoms; R9 and R10 are H, R11is H or a straight, branched, or cyclic alkyl group of 1 to 20 carbons,and R12 and R13 are a straight, branched, or cyclic alkyl or fluorinatedalkyl group of 1 to 20 carbons; and R14 and R15 are H, and R16 is H or astraight, branched, or cyclic alkyl group of 1 to 20 carbons, and R17and R18 are a straight, branched, or cyclic alkyl or fluorinated alkylgroup of 1 to 20 carbons; performing a pre-exposure bake on the resistlayer; exposing the resist-coated substrate; and developing the exposedsubstrate with a developing solution.
 2. The method of claim 1, whereinafter developing, the resist layer loses about 50 A of its previousthickness due to removal of the switchable polymer.
 3. The method ofclaim 1, wherein during the pre-exposure bake, the resist layer isseparated into a first layer containing the resist polymer and a secondlayer containing the switchable polymer.
 4. The method of claim 3,wherein the second layer has a thickness between about 10 A to about1000 A.
 5. The method of claim 4, wherein after developing, thethickness of the second layer is reduced by less than about 400 A. 6.The method of claim 1, wherein the lithography is an immersionlithography and wherein a portion, but not all, of the resist layerbecomes hydrophilic in response to an immersion fluid used in theimmersion lithography.
 7. The method of claim 1, wherein the exposing isoptical and of a wavelength from a group associated with KrF, ArF,extreme ultra-violet (EUV), and e-beam.
 8. The method of claim 1,wherein the structure of the switchable polymer includes one of a lowermolecular weight than the resist polymer, a different polarity from theresist polymer, a different hydrophobic/hydrophilic ratio from theresist polymer, a different solubility from the resist polymer, or adifferent hydrogen bonding from the resist polymer.
 9. A method forperforming lithography on a semiconductor substrate, the methodcomprising: coating a resist layer on the substrate, wherein the resistlayer comprises a resist polymer configured to turn soluble to a basesolution in response to reaction with an acid, a quencher baseconfigured to stop a chemical amplified reaction during a post-exposurebaking step, and a switchable polymer that includes one of:

wherein R1, R2, and R3 are H and R4 is a fluorinated alkyl group of 1 to20 carbon atoms; R5, R6, and R7 are H and R8 is a straight chainfluorinated alkyl group of 1 to 20 carbon atoms; R9 and R10 are H, R11is H or a straight, branched, or cyclic alkyl group of 1 to 20 carbons,and R12 and R13 are a straight, branched, or cyclic alkyl or fluorinatedalkyl group of 1 to 20 carbons; and R14 and R15 are H, and R16 is H or astraight, branched, or cyclic alkyl group of 1 to 20 carbons, and R17and R18 are a straight, branched, or cyclic alkyl or fluorinated alkylgroup of 1 to 20 carbons; performing a pre-exposure bake on the resistlayer; exposing the resist-coated substrate; and developing the exposedsubstrate with a developing solution.
 10. The method of claim 9, whereinduring the pre-exposure bake, the resist layer is separated into a firstlayer containing the resist polymer and a second layer containing theswitchable polymer.
 11. The method of claim 10, wherein the second layerhas a thickness between about 10 A to about 1000 A.
 12. The method ofclaim 11, wherein after developing, the thickness of the second layer isreduced by less than about 400 A.
 13. The method of claim 9, wherein thelithography is an immersion lithography and wherein a portion, but notall, of the resist layer becomes hydrophilic in response to an immersionfluid used in the immersion lithography.
 14. The method of claim 9,wherein the exposing is optical and of a wavelength from a groupassociated with KrF, ArF, extreme ultra-violet (EUV), and e-beam. 15.The method of claim 9, wherein the structure of the switchable polymerincludes one of a lower molecular weight than the resist polymer, adifferent polarity from the resist polymer, a differenthydrophobic/hydrophilic ratio from the resist polymer, a differentsolubility from the resist polymer, or a different hydrogen bonding fromthe resist polymer.
 16. A method for performing lithography on asemiconductor substrate, the method comprising: coating a resist layeron the substrate, wherein the resist layer comprises a resist polymerconfigured to turn soluble to a base solution in response to reactionwith an acid and a switchable polymer that includes one of:

wherein R1, R2, and R3 are H and R4 is a fluorinated alkyl group of 1 to20 carbon atoms; R5, R6, and R7 are H and R8 is a straight chainfluorinated alkyl group of 1 to 20 carbon atoms; R9 and R10 are H, R11is H or a straight, branched, or cyclic alkyl group of 1 to 20 carbons,and R12 and R13 are a straight, branched, or cyclic alkyl or fluorinatedalkyl group of 1 to 20 carbons; and R14 and R15 are H, and R16 is H or astraight, branched, or cyclic alkyl group of 1 to 20 carbons, and R17and R18 are a straight, branched, or cyclic alkyl or fluorinated alkylgroup of 1 to 20 carbons, performing a pre-exposure bake on the resistlayer; immersing the substrate in an immersion exposure liquid; exposingthe immersed resist-coated substrate to an ultraviolet light source,extreme ultraviolet light source, or e-beam laser; and developing theexposed substrate with a developing solution.
 17. The method of claim16, wherein during the pre-exposure bake, the resist layer is separatedinto a first layer containing the resist polymer and a second layercontaining the switchable polymer.
 18. The method of claim 17, whereinthe second layer has a thickness between about 10 A to about 1000 A. 19.The method of claim 18, wherein, after developing, the thickness of thesecond layer is reduced by less than about 400 A.
 20. The method ofclaim 16, wherein the structure of the switchable polymer includes oneof a lower molecular weight than the resist polymer, a differentpolarity from the resist polymer, a different hydrophobic/hydrophilicratio from the resist polymer, a different solubility from the resistpolymer, or a different hydrogen bonding from the resist polymer.